There has heretofore been known a traffic light detection device that detects a traffic light from an image taken by a camera (see Japanese Patent Application Publication No. 2005-301518). In Japanese Patent Application Publication No. 2005-301518, a signal lamp candidate is detected from the image based on the color and shape of a signal lamp, and it is determined whether or not the signal lamp candidate is flashing with a predetermined period.
When a vehicle equipped with a camera is on the move, positions of brightness edges included in an image taken in motion also move. Thus, step responses of brightness occur in regions where the brightness edges have moved, thus generating noise having wide frequency components. When pixels whose brightness changes with a predetermined period are extracted as a signal lamp, the noise having wide frequency components is erroneously recognized as the signal lamp in some cases.